This invention relates generally to gas turbine engines and, more particularly, to variable exhaust nozzles therefor.
For multimission aircraft applications, the exhaust nozzle operating conditions vary significantly during the mission. In order to maintain high performance over the entire operating range of the aircraft, the exhaust nozzle configuration can become very complex which, in turn, results in increased weight, cost and reliability.
Most current multimission aircraft applications employ engines with convergent-divergent nozzles to meet the system requirements. Characteristically, these nozzles are variable in area at both the nozzle throat (at the downstream end of the convergent nozzle) and at the nozzle exit (at the downstream end of the divergent flap). Ideally, the operation of the nozzle will provide a nozzle throat/exit area ratio schedule which is optimized for the design cycle of the engine. Further, this relationship should provide efficient control at both low subsonic and high supersonic flight conditions while exhibiting low afterbody drag.
One approach has been to design the nozzle so that the area ratio schedule is fixed (e.g., where the convergent and divergent sections are integral). However, it has been found that such an approach tends to limit the flexibility for optimizing the area ratio schedule for the initial cycle, and further limits the flexibility for accommodating changes in cycle and mission requirements which frequently occur during and after development of the system.
Another approach has been to actuate the divergent flap and the convergent flap separately, as by way of separate cams acting on both the inner and outer nozzle flaps. Although such a nozzle has flexibility for optimizing the area ratio schedule and can accommodate changes in cycle and mission requirements, the system offers penalties by way of complexity, weight and cost.
It is therefore an object of the present invention to provide a variable area exhaust nozzle which is suitable for multimission aircraft applications.
Another object of the present invention is the provision for a variable area exhaust nozzle which exhibits a favorable nozzle throat/exit area ratio schedule over an entire engine design cycle.
Still another object of the present invention is the provision in an aircraft engine for a variable area nozzle which is flexible for selection and adjustment of area ratio schedules to match a variety of engine cycles.
Yet another object of the present invention is the provision in a variable area exhaust nozzle for favorable throat/exit area ratios and low afterbody drag during both subsonic and high supersonic flight conditions.
Yet another object of the present invention is the provision of a variable area exhaust nozzle which is simple in operation, light in weight, and economical to manufacture.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.